In electrography or ionography, an electrostatic latent image is formed on a dielectric imaging surface of an imaging layer (electroreceptor) by various techniques such as by ion stream (ionography), stylus, shaped electrode, and the like. Development of the electrostatic latent image may be effected by contacting the imaging surface with electrostatically attractable marking or toner particles whereby the particles deposit on the imaging surface in conformance to the latent image. The deposited particles may be transferred to a receiving member (such as paper) and the imaging surface may be cleaned and cycled through additional imaging and development cycles.
In addition, it is often important that electrostatographic imaging members be compatible with various imaging systems. Modern copiers and printers employ various development systems utilizing liquid or dry developers for producing color or black and white images. It is desirable to create an imaging member which will function in as many imaging systems as possible because not all existing imaging members function equally effectively in all environments. Ideally, an imaging member would be created to function equally effectively in liquid or dry developers and be useful in color or black or white copying systems.
Ionography is, in some respects, similar to the more familiar form of imaging used in electrophotography. However, the two types of imaging are fundamentally different. In electrophotography, an electrophotographic member containing a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging its surface. The member is then exposed to a pattern of activating electromagnetic radiation such as light. The electrophotographic member is insulating in the dark and conductive in light. The radiation therefore selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated areas. Thus, charge is permitted to flow through the imaging member. The electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the electrophotographic member to a support such as paper. This imaging process may be repeated many times with reusable photoconductive insulating layers.
Ionographic imaging members differ in many respects from the above-described and other electrophotographic imaging members. The imaging member of ionographic devices is electrically insulating so that charge applied thereto does not disappear prior to development. Charge flow through the imaging member is undesirable since charge may become trapped, resulting in a failure of the device. Ionographic receivers possess negligible, if any, photosensitivity. The absence of photosensitivity provides considerable advantages in ionographic applications. For example, the electroreceptor enclosure does not have to be completely impermeable to light, and radiant fusing can be used without having to shield the receptor from stray radiation. Also, the level of charge decay (the loss of surface potential due to charge redistribution or opposite charge recombination) in these ionographic receivers is characteristically low, thus providing a constant voltage profile on the receiver surface over extended time periods.
However, ionographic imaging members generally suffer from a number of disadvantages. In an ionographic machine, the electroreceptor comes into contact with development and cleaning sub-systems. Also, paper contacts the surface of the electroreceptor in the transfer zone. Thus, an electroreceptor material which has good electrical properties for ionographic applications, Le., electrically insulating, may be triboelectrically incompatible with the sub-systems of the ionographic machine. For example, a particularly good electroreceptor dielectric material may be incompatible with toner contact because of high triboelectric charging. This incompatibility leads to, among other problems, cleaning failures because of the poor toner release properties of the dielectric material.
A further problem with many ionographic imaging members involves high charge decay and charge trapping. Materials having a high dielectric constant and good toner release properties may suffer from high surface charge decay and charge trapping. For example, materials having a high dielectric constant, such as polyvinyl fluoride, have high charge decay rates and bulk charge trapping.
It is also desirable for exposed surfaces of a dielectric receiver to have good wear, abrasion, scratch, and chemical resistance properties. Organic film forming resins used in the dielectric imaging layer are subject to wear, abrasions, scratches, and chemical attack by liquid developers which adversely affect the response of the dielectric receiver.
It is also desirable in certain applications involving liquid developers to condition the developed toner image by removing the excess liquid carrier fluid associated with the developed image so as to increase toner solids. An electrographic imaging member which retains an image charge when heated electrostatically holds the toner in position while the toner carrier fluid is removed for example by evaporation thereby improving image resolution.
The above and other problems limit the use of various materials in ionographic charge receivers. The problems are further complicated in that there are very few materials with high dielectric constants which have the desirable properties for ionographic imaging. Thus, the present invention addresses the problems described herein.
Conventional printing machines and electrographic imaging members are disclosed in Gundlach et al., U.S. Pat. No. 5,493,373, Mammino et al., U.S. Pat. No. 5,338,587, Mammino et al. U.S. Pat. No. 5,096,796, and Mammino et al., U.S. Pat. No. 5,266,431.
An illustrative fusing system is disclosed in Heeks et al., U.S. Pat. No. 4,777,087.